Intraocular diseases such as diseases of a retina, an optic nerve or a vitreous body are often intractable, and a development of an effective treatment method is eagerly desired. Though ocular diseases are most generally treated by instillation of drugs, the drugs are hardly delivered to the intraocular tissues such as a retina, rendering the treatment of the intraocular diseases all the more difficult.
In view of this, a method of administering a drug directly to a specific site of a body was attempted. For example, a technique for administering a liposome or a microsphere containing a drug to intraocular tissues such as a vitreous body was reported (Published Japanese Translation of PCT No. 508369/1994, Japanese Laid-open Patent Publication No. 221322/1992 and the like).
However, it is not easy to control release of the drug by using the liposome. The liposome and the microsphere have large particle diameters. Accordingly, when they are administered to the intraocular tissues such as the vitreous body, transparency in the vitreous body sometimes cannot be maintained.
On the other hand, when the drug is administered orally, the drug is easily absorbed and metabolized in a stomach, a small intestine, a large intestine, a liver. Accordingly, it is difficult to deliver the drug to a specific site to attain a concentration at which drug efficacy is exhibited.
From these facts, it is an important subject to prepare substances which are excellent in delivery and enable drugs to be retained in a body effectively over a long period and to create a drug delivery system using the substances.